1. Field of Invention
The present invention relates to an LED driver with direct AC-DC conversion and control function, and a method and an integrated circuit therefor.
2. Description of Related Art
FIG. 1 shows prior art circuitry to provide a regulated current output to LEDs from an AC power supply. It requires an AC-DC power converter 10 which converts an AC power to a regulated DC voltage, and an LED driver circuit 20 which receives the regulated DC voltage and provides a regulated current output. The AC-DC power converter 10 comprises a transformer 13, a primary side circuit 11, a secondary side circuit 12, a bridge rectifier 14, and other discrete devices such as capacitors and diodes, etc. (not shown). The secondary side circuit 12 detects its output voltage, and provides a corresponding feedback signal to a switching control circuit PWM in the primary side circuit 11 through photo coupling. The switching control circuit PWM controls the operation of a power switch P in the primary side circuit 11, so that the output voltage of the AC-DC power converter 10 is regulated.
The aforementioned prior art has the following drawback. Because it requires an AC-DC power converter 10 to generate a regulated voltage and an LED driver 20 to control current through LEDs according to the regulated voltage, this prior art needs at least three integrated circuit chips: the primary side circuit 11, the secondary side circuit 12, and the LED driver 20; it is not cost-effective.
For AC-DC power conversion, there is another prior art called LLC (inductor-inductor-capacitor) structure. Referring to FIG. 2, in addition to two inductors in the transformer 13, an additional capacitor is provided, so it is called LLC structure. In this LLC structure, the primary side circuit 11a is slightly different from that in FIG. 1; the voltage conversion by the transformer is controlled by an LLC controller 111 which controls the operations of two power switches P1 and P2 to regulate the output voltage. Although the overall architecture is slightly different from the first prior art, the drawback is the same, i.e., this prior art needs at least three integrated circuit chips: the primary side circuit 11a, the secondary side circuit 12, and the LED driver 20; it is not cost-effective.
In view of the foregoing, the present invention provides an LED driver with direct AC-DC conversion and control function, and a method and an integrated circuit therefor. Furthermore, the integrated circuit of the present invention can be applied not only to circuitry performing AC-DC conversion, but also to circuitry performing DC-DC conversion.